Trouble connecting to server on multiple devices

Welcome to the ODK forum, @catlan! We're glad you're here. When you get a chance, please introduce yourself on this forum thread. I'd also encourage you to add a real picture as your avatar because it helps build community!

Is your Aggregate server in the cloud or on local hardware? Can you provide some more details about your setup? Is your phone accessing the server while on the same local network? Are you using a private IP address or a public IP address?